A twin phaser can be used in an internal combustion engine in the drive train from the engine crankshaft to camshaft lobes operating on two different sets of gas exchange valves of the engine. The two sets may be the intake valves and the exhaust valves, respectively. Alternatively, in an engine with multiple valves per cylinder, both sets of valves may be valves of the same type, e.g., intake valves. The present invention is primarily concerned with the construction of the twin phaser and not with the manner in which the two outputs are used in any specific application.
Various designs of phaser have been proposed in the prior art which are operated mechanically, electrically or hydraulically. The present invention relates to hydraulically controlled phasers, examples of which are vane-type phasers. In vane-type phasers, a radial vane connected to one of two members of which the relative phase is to be varied, separates two working chambers within an arcuate cavity defined by the other member.
Twin phasers that are controlled hydraulically generally need four separate oil feeds, as each of the two outputs requires a hydraulic supply line and a return line. Connecting four oil feeds to the cam phaser is complicated because four sealed interfaces are required between the moving parts on the cam/phaser and the stationary parts on the engine.
The same problem is experienced not only with phasers that are hydraulically operated, i.e., that rely on an external pressure supply, but also with other types of phaser, such as, for example, with phasers that rely on differential pressures in the working chambers of the phaser resulting from torque reversals and clutch type phasers as described in EP1216344.
The term “hydraulically controlled” is intended to include all of these phaser types.
Connecting four oil feeds or control lines to a cam phaser can be achieved using an oil-feed manifold, mounted to the front cover and connected to the front of the cam phaser, as described, for example, in U.S. Pat. No. 6,247,436 and in GB 2,401,150. On occasions, however, there is not the packaging space for this to be achieved, especially in an overhead camshaft application. Furthermore, it may be undesirable in some cases to feed pressurised oil through passageways in the front cover.
It has also previously been proposed to construct the oil feeds so that they pass through the camshaft via grooves and passageways formed in the cam bearings. As is discussed below, this approach also raises certain issues.
FIG. 11 of U.S. Pat. No. 7,610,890 (Mahle) shows four adjacent radial grooves cut into the front camshaft bearing. This proposal requires a very large or long front cam bearing to accommodate the four feeds and enough area for it to still act as a bearing surface.
FIG. 1 of U.S. Pat. No. 7,503,293 (Mahle) shows how the two front bearings in a concentric camshaft can be used to convey oil to a twin phaser. In this layout, there are increased opportunities for leakage as oil can leak out of slots in tube 6 where pin 7 moves. The complexity of this proposal also has cost implications.
FIG. 2 of US 2007/0295,296 (Mahle) shows yet another alternative way of conveying the four oil feeds.
It is preferred for the design of the hydraulic control system to reduce the number of oil feeds to the phaser. For a single-output cam phaser, it has been suggested that if the oil control/spool valve is integrated into the body of the cam phaser (rather than having it somewhere in the cylinder head or cylinder block), then only a single oil feed is required.
U.S. Pat. No. 6,571,757 shows such an integrated spool design for a cam-torque actuated cam phaser where a single spool valve is located on the axis of the phaser and its axial position is controlled by an actuator mounted onto the front cover. By moving the spool valve axially, different oil channels are connected and the phaser advances or retards.
This type of design is suitable for a single-output phaser but it is relatively complex for a dual-output device because the front actuator needs to control the axial position of two in-line spool valves independently. Gaining access to the rear spool valve and being able to package two spool valves in line within the confines of the phaser envelope presents difficulty.
U.S. Pat. No. 7,444,968 shows a twin-spool design for a dual independent torque actuated phaser.